1. Field of the Invention
This invention relates to a heat recording apparatus for applying heat to a transfer sheet carrying thereon, for example, a heat-meltable transfer material (heat-meltable ink) in accordance with image information to thereby accomplish transfer recording on a recording sheet.
2. Description of the Prior Art
Popular heat transfer recording apparatuses include a color recording apparatus such as is shown in FIG. 1 of the accompanying drawings.
In FIG. 1, reference numeral 1 designates a recording sheet paid away from a supply roll 3 and conveyed by pairs of rollers 2.sub.1 -2.sub.4. Reference numerals 4.sub.1, 4.sub.2 and 4.sub.3 denote heat transfer sheets to which heat transfer ink layers are applied. The sheet 4.sub.1 has a cyan heat transfer ink layer, the sheet 4.sub.2 has a magenta heat transfer ink layer, and the sheet 4.sub.3 has a yellow heat transfer ink layer. The heat transfer sheets are paid away from supply rolls 5.sub.1 -5.sub.3, respectively, and taken up by take-up rolls 6.sub.1 -6.sub.3, respectively. Reference numerals 7.sub.1, 7.sub.2 and 7.sub.3 designate thermal heads. The recording sheet and the heat transfer sheets are pressed between the thermal heads and platen rollers 8.sub.1, 8.sub.2, 8.sub.3.
When color recording by the three colors is to be effected, the head 7.sub.1 is first driven and cyan is heat-transferred to and recorded on the recording sheet on which cyan has been recorded is fed to the head 7.sub.2 and there magenta is heat-transferred and recorded while being superposed on the cyan ink, whereafter the area of the recording sheet on which there two colors have been recorded is fed to the head 7.sub.3 and there yellow is heat-transferred and recorded while being further superposed on the cyan and magenta inks. Thus, the area of the recording sheet on which recording has been completed is cut to a predetermined length by a cutter 9. When one head is being driven, the other two heads are put out of service.
In the apparatus of FIG. 1, the heat transfer sheets 4.sub.1 -4.sub.3 are taken up onto the take-up rolls 6.sub.1 -6.sub.3, respectively, by these rolls being driven, but if the rolls 6.sub.1 -6.sub.3 are strongly driven, conveyance of the heat transfer sheets 4.sub.1 -4.sub.3 will become unstable because the sheets 4.sub.1 -4.sub.3 are very thin, and this will particularly be so where the width of the sheets 4.sub.1 -4.sub.3 is great enough to cover paper of B5 or A4 size. For this reason, the sheets 4.sub.1 -4.sub.3 are moved by the friction force thereof with respect to the recording sheet 1 rather than by the tensile force of the rolls 6.sub.1 -6.sub.3 in the portions wherein the sheets 4.sub.1 -4.sub.3 bear against the heads 7.sub.1 -7.sub.3, respectively.
The apparatus of FIG. 1 suffers from the following problems. First, synchronized conveyance of the heat transfer sheets and the recording sheet resorts chiefly to the friction force between the sheets in the portions wherein they bear against the heads 7.sub.1 -7.sub.3 and therefore, the friction force is varied by the heat during the operation of the heads and slippage is liable to occur between the sheets. Also, dilation of the sheets is liable to occur due to the heat applied to the sheets by the heads 7.sub.1 -7.sub.3 or wrinkling of the thin heat transfer sheet is liable to occur due to contraction stress, and this is more conspicuous as the heat transfer sheets become wider enough to cover recording sheet of large size such as B5 or A4 size. All of these things deteribrate the quality of the image recorded on the recording sheet. Also, the sheets are separated from each other immediately after the heat transfer materials of the heat transfer sheets have been heated and melted by the heads 7.sub.1 -7.sub.3 and therefore, there is no sufficient time for the heat transfer materials to become attached to the recording sheet, and this also leads to unsatisfactory transfer From these facts, the apparatus of FIG. 1 is not suitable for high-speed recording.
On the other hand, there is an apparatus in which, unlike the apparatus of the above-described type, for example, the platen drum is provided with a pawl so that the leading end edge of a cut recording sheet is seized by the pawl and the recording sheet is wound on the platen drum and a heat generating head is urged against the thus wound recording sheet with a heat transfer sheet interposed therebetween to thereby accomplish heat transfer recording.
In such an apparatus, however, to automate the seizure of the recording sheet by the pawl, the mechanism is generally complicated, and this has led to bulkiness and increased cost of the apparatus.
Also, in the apparatuses according to the prior art, when multi-color superposition recording is to be effected on the recording sheet, it has been very difficult to accomplish the multi-color super-position recording accurately without misregistration.